Impact of spinning droplets onto superhydrophobic surfaces: Asymmetric tumbling rapid rebound

The impact of spinning droplets is a broader prevalence in practical scenarios, yet it remains insufficiently explored. This rotational mode engenders distinct asymmetric dynamics that are expected to generate novel phenomena and alter the contact time, which holds significant implications for liquid dispersal and surface cleaning.

The impact dynamics of spinning droplets onto superhydrophobic surfaces was investigated over wide ranges of Weber number (We) and dimensionless angular velocity (Ω), with computational results validated by high-speed imaging experiments, and the impact process was further analyzed theoretically.

The spinning motion of droplets induces two novel rebound scenarios and can significantly reduce the droplet-wall contact time by up to approximately 40% relative to classical normal impacts. Specifically, the front-raise tumbling rebound occurs at a lower Ω and is caused by the unsymmetrical capillary force, while the rear-raise tumbling rebound emerges at a higher Ω and is attributed to the rotational inertia. Counterintuitively, the direction of the droplet's detachment angular momentum may be opposite to the visually observed tumbling rebound, owing to the reversed torque from inertial impact. We establish a unified theoretical model based on We and Ω to explain and predict the asymmetric spreading and rapid rebound.